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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <title>page_188</title> <link rel="stylesheet" href="reset.css" type="text/css" media="all"> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> </head> <body> <table summary="top nav" border="0" width="100%"> <tr> <td align="left" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_187.html">< previous page</a></td> <td id="ebook_previous" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_188</strong></td> <td align="right" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_189.html">next page ></a></td> </tr> <tr> <td id="ebook_page" align="left" colspan="3" style="background: #ffffff; padding: 20px;"> <table border="0" width="100%" cellpadding="0"><tr><td align="center"> <table border="0" cellpadding="2" cellspacing="0" width="100%"><tr><td align="left"></td> <td align="right"></td> </tr></table></td></tr><tr><td align="left"><p></p><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="right"><font face="Times New Roman, Times, Serif" size="2" color="#FF0000">Page 188</font></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">three gyros and three accelerometers. The error equations are derived with sufficient detail to allow the reader to extend the error analysis to alternative implementations.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">A pure INS implementation can suffer from unbounded growth in the position and the velocity errors due to the integration of inertial measurements that will contain various forms of error. The pure INS implementations described in this chapter can either be designed around high-quality inertial instruments to decrease the rate of error growth or be augmented with additional sensors to allow the estimation of INS state errors (i.e, inertial aiding). Such aided inertial systems are discussed in Chap. 7.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">The chapter is organized as follows. In Sec. 6.1 some basic information about accelerometers is given that is required for the subsequent analysis. In Sec. 6.2 the differential equations for position and velocity are derived as functions of the measured specific force and angular rates. In Sec. 6.3 the navigation mechanization equations are summarized that apply to the local tangent-plane, north-pointing INS. In Sec. 6.4 the error equations for the basic nine states of the same INS are derived. The error equations are necessary both for an understanding of the dynamics of the INS error growth and for implementation of state-space error-estimation schemes. In Sec. 6.5 the derivation of the accelerometer and gyro error models are presented, which are necessary for construction of truth models for the analysis of system performance. In Sec. 6.6 the earth geoid and models of the earth gravity vector are discussed. The sensitivity of the gravity vector to position is analyzed and accounted for in the error dynamic matrix. In Sec. 6.7, the detailed error models of the previous sections are simplified into the three- and the four-state simplified INS error models that have been used in several examples in the previous chapters. Although the simplified error models do not have the fidelity required of a truth model to predict expected performance, the simplified models are useful for illustrating basic underlying ideas without the complexity of the more detailed models. In Sec. 6.8 methods for determining the initial conditions necessary for solving the INS mechanization equations are discussed. In Sec. 6.9 the topic of lever-arm compensation is discussed. Although lever-arm compensation is not a direct subtopic of inertial navigation, lever-arm issues must be realized and compensated for in INS initialization and aiding systems.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="17"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">6.1<br />Accelerometers</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">The objective in this section is to describe the basic operation of an ideal accelerometer and to define the concept of specific force. A thorough discussion of accelerometer errors is presented in Sec. 6.5.1.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">Imagine an accelerometer as a spring mass damper system in which the three-dimensional position of the proof mass relative to the accelerometer casing R</font><font face="Times New Roman, Times, Serif" size="1"><sub><i>c</i></sub></font><font face="Times New Roman, Times, Serif" size="3"> can be perfectly measured. Then, by Newton's laws, the dynamic equation for an accelerometer in free space (no rotation, no gravitation) is</font><font face="Times New Roman, Times, Serif" size="3" color="#FFFF00"></font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3"><img src="0c528693308df62cba89ce0ce7bb74af.gif" border="0" alt="0188-01.GIF" width="305" height="33" /></font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td></tr></table><p><font size="0"></font></p>聽 </td> </tr> <tr> <td align="left" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_187.html">< previous page</a></td> <td id="ebook_next" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_188</strong></td> <td align="right" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_189.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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